Mongoose更新Teacher文档students子文档数组的payment字段后，save()未持久化变更的问题求助

我最近用Mongoose更新Teacher文档时碰到了个棘手的问题：我想修改Teacher文档里students子文档数组中的payment字段，在调用await teacher.save()之前，console.log(teacher)和console.log(teacher.students)都能正确显示修改后的内容，但保存完成后，数据库里的payment字段完全没变化！而且代码全程没抛出任何错误，看起来像是“成功”执行了保存，就是变更根本没持久化到数据库里。

我的路由代码 #

// Route 5: Update student payment types
router.put("/api/analytics/students/payment-types", passport.authenticate("jwt", { session: false }), async (req, res) => {
  const { user } = req;
  const { students } = req.body;

  try {
    const teacher = await Teacher.findOne({ user: user._id });

    if (!teacher) {
      return res.status(404).json({ message: "Teacher not found" });
    }

    // Validation
    if (!Array.isArray(students)) {
      return res.status(400).json({ message: "'students' must be an array" });
    }

    // Updating
    for (const studentUpdate of students) {
      if (!studentUpdate.studentId || !mongoose.Types.ObjectId.isValid(studentUpdate.studentId)) {
        return res.status(400).json({ message: `Invalid or missing studentId: ${studentUpdate.studentId}` });
      }

      if (studentUpdate.paymentType && !mongoose.Types.ObjectId.isValid(studentUpdate.paymentType)) {
        return res.status(400).json({ message: `Invalid paymentType for student ${studentUpdate.studentId}` });
      }

      const studentIndex = teacher.students.findIndex(
        (s) => s.studentId.toString() === studentUpdate.studentId
      );

      if (studentIndex !== -1) {
        teacher.students[studentIndex].payment = studentUpdate.paymentType || null;
      }
    }

    teacher.markModified("students");
    console.log(teacher.isModified());
    console.log(teacher.students);
    await teacher.save();

    res.status(200).json({ message: "Student payment types updated successfully", success: true });
  } catch (error) {
    console.error("Error updating payment types:", error);
    res.status(500).json({ message: "Error updating student payment types" });
  }
});

Teacher模型定义 #

const TeacherSchema = new mongoose.Schema({
  // 其他字段
  students: [
    {
      studentId: {
        type: ObjectId,
        ref: "User",
        required: true,
      },
      payment: {
        type: ObjectId,
        required: false,
      },
    },
  ],
});

我已经尝试过的排查步骤 #

• 确认代码中已经正确定位到目标学生，并且修改后的payment字段值在日志中能正常显示
• 在save()之前主动调用了teacher.markModified("students")，甚至试过标记更具体的路径比如teacher.markModified("students.0.payment")
• 反复核对模型定义，确认students子文档数组里确实存在payment字段
• 打印teacher.isModified()返回true，说明Mongoose确实检测到了文档变更

现在实在搞不懂为什么save()操作看似成功，数据库里的内容却纹丝不动。有没有朋友遇到过类似的问题？或者能帮我分析下可能的原因吗？

内容来源于stack exchange